In image display devices provided with backlights such as liquid crystal display devices, by controlling the luminances of the backlights on the basis of input images, the power consumption of the backlights can be suppressed and the image quality of a displayed image can be improved. In particular, by dividing a screen into a plurality of areas and controlling the luminances of backlight sources corresponding to the areas on the basis of portions of an input image within the areas, it is rendered possible to achieve lower power consumption and higher image quality. Hereinafter, such a method for driving a display panel while controlling the luminances of backlight sources on the basis of an input image in each area will be referred to as “area-active drive”.
Liquid crystal display devices that perform area-active drive use, for example, LEDs (light emitting diodes) of three RGB colors or white LEDs, as backlight sources. Luminances upon emission (hereinafter, referred to as “emission luminances”) of LEDs corresponding to areas are obtained on the basis of, for example, maximum or mean values of pixel luminances within the areas, and are provided to a backlight driver circuit as LED data. In addition, display data (data for controlling the light transmittance of the liquid crystal) is generated on the basis of the LED data and an input image, and the display data is provided to a driver circuit for a liquid crystal panel.
According to a liquid crystal display device such as that described above, suitable display data and LED data are obtained based on an input image, and the light transmittances of liquid crystals are controlled based on the display data, and the emission luminances of LEDs provided in respective areas are controlled based on the LED data, whereby the input image can be displayed on the liquid crystal panel. When the luminance of pixels in an area is low, by reducing the emission luminance of LEDs provided in the area, the power consumption of the backlight can be reduced.
Note that the following conventional technology document is known in the art relevant to the present invention. International Publication WO2009/096068 pamphlet discloses an invention of an image display device in which, to inhibit flickering from occurring when displaying dynamic images, an emission luminance of LEDs is obtained for each area within the range between upper and lower limits calculated on the basis of an average luminance level among images for one frame.